Enclosed coaxial antenna



Q @NQSS REH'EWE SEMH RGQM June 21, 1960 A. E. RATKEVICH 2,942,265

ENCLOSED COAXIAL ANTENNA Filed March 51, 1958 INVENTOR.

ADAM E. RATKEV ICH United States Patent ENCLOSED COAXIAL ANTENNA Adam E. Ratkevich, San Diego, Calif., assignor to Ryan Aeronautical Co., San Diego, Calif.

Filed Maru 31, 1958, Ser. No. 725,435

4 Claims. (Cl. 343-779) The present invention relates generally to microwave antennas and more particularly to an enclosed coaxial antenna.

The primary object of this invention is to provide an antenna having parabolic transmitter and receiver reflectors mounted in fixed concentric relation, the assembly being totally enclosed by dome-like members and the whole being secured together into an extremely rigid unitary structure.

Another object of this invention is to provide an antenna which utilizes a folded path for the microwave energy in the receiver reflector system so that a relatively large reflector may be used in a very compact assembly.

Still another object of this invention is to provide an enclosed coaxial antenna which, due to its rigid unitary structure, has very low vibration characteristics and so minimizes microphonics in the antenna system.

Finally, it is an object to provide an enclosed coaxial antenna of the aforementioned character which is simple to manufacture and which will give generally eflicient and durable service.

With these and other objects definitely in view, this invention consists in the novel construction, combination and arrangement of elements and portions, as will be hereinafter fully described in the specification, particularly pointed out in the claims, and illustrated in the drawing which forms a material part of this disclosure, and in which:

Figure l is a front elevation view of the antenna; and

Figure 2 is a sectional view taken on the line 2-2 of Figure 1.

Similar characters of reference indicate similar or identical elements and portions throughout the specification and throughout the views of the drawing.

Referring now to the structural details shown in the drawing, the basic antenna is similar to that disclosed in my copending application for a coaxial antenna filed March 31, 1958, Serial No. 725,434, and comprises a large, generally parabolic receiver reflector and a smaller parabolic transmitter reflector 12. The trans mitter reflector 12 is fixed in one end of a support cylinder 14, the other end of which is fixed to the receiver reflector 10, so that the transmitter reflector, support cylinder and receiver reflector are coaxial. The central portion 18 of the receiver reflector 10, enclosed by the support cylinder 14, is flat and to this flat portion is secured the antenna servo mechanism indicated in broken line at 20. Fixed inside the support cylinder 14 adjacent the transmitter reflector 12 is a flat plane reflector 22 having its reflecting surface 24 directed toward the flat portion 18. The annular parabolic portion 26 of the receiver reflector 10 has a reflective layer 28 and the transmiter reflector 12 has a reflective layer 30.

The reflectors 10, 12 and 22 and the support cylinder 14 are preferably made of plastic or similar material, laminated or of cored construction and all bonded together into a rigid assembly. The reflective surfaces may 2,942,265 Patented June 21, 1960 e be applied by spraying or otherwise depositing a metallic coating on the appropriate parts.

The transmitter reflector 12 is illuminated in a conventional manner by a feed 34 mounted at the end of a waveguide 36, which extends radially and rearwardly and is attached to the edges of both reflectors 12 and 10. The receiver feed 38 is mounted on the flat portion 18 inside the support cylinder 14.

The reflector assembly is enclosed by a dome-like structure 39 comprising a dome cap 40 and a dome ring 42. The dome cap 40 covers the transmitter reflector 12 and actually fits inside the end of the support cylinder 14 which extends beyond said reflector to provide an isolating shroud 44. The dome ring 42 extends from the outer face of the isolating shroud 44 to the periphery of the receiver reflector 10 and eifectively encloses that reflector. The dome cap 40 and dome ring 42 have a continuous outer surface which may be spheroidal in shape for simplicity of manufacture. Due to the difference in angles of incidence of the microwaves passing through the dome structure, the cap and ring portions are of different thicknesses. Thus the dome cap 40 is substantially thinner than the dome ring 42. The ideal dome would have a tapered thickness corresponding to the degree of curvature relative to the direction of microwave emission, the formula for the thickness being well known in the art. However, for simplicity, the average angles of incidence for the transmitter reflector 12 and receiver reflector 10 may be determined and the thicknesses of the dome cap 40 and dome ring 42, respectively, calculated to suit those average figures.

For additional rigidity, the waveguide 36 is bonded to the inner surface of the dome cap 40 and dome ring 42. The isolating shroud 44 has a metallic coating 46 extending from the reflective coating 30 of the transmitter reflector 12 and also continuing over a portion of the outer surface of the support cylinder 14. This reflective isolating shroud 44 projects in the form of a ring ahead of the dome structure 39 and provides an electromagnetic shield between the transmitter reflector 12 and the receiver reflector 10, to prevent leakage of microwave energy from one to the other. In fact the actual length of the isolating shroud 44 is such that the energy radiated directly from the feed 34 arrives at the edge of the shroud substantially out of phase with the energy reflected from the transmitter reflector 12, so tending to cancel and reduce the possibility of energy leakage to the receiver reflector 10 by diffraction about the edge.

The transmitted microwave energy is beamed out from the transmitter reflector 12 in the normal manner. The echo, or received signal, is collected by the receiver reflector 10 and reflected through the support cylinder 14 to the plane reflector 22, which is turn reflects it to the receiver feed 38. By using this folded path for the received signal, the axial length of the antenna assembly is greatly reduced, since the normal focal point for the large shallow receiver reflector 10 would be some distance ahead of the physical limits of the antenna. By returning the received signal from the plane reflector 22, a new effective focal point is created adjacent the flat portion 18 and the receiver feed 38 is mounted at this point. The flat plane reflector 22 has been found to be very effective and provides excellent edge illumination for the receiver reflector 10.

It should be understood that the dome structure 39 is not intended as a streamlining or wind protecting element, since the antenna is designed for mounting inside a protective nose cover or the like, thus the projecting isolating shroud 44 is not drag inducing. The antenna is rotated or otherwise moved by the servo mechanism 20 to provide conventional scanning. The entire assembly is bonded together as a rigid unitary structure and has no moving parts in itself, the dome structure 39 merely being a supporting means for the active antenna components. Due to its rigidity, the antenna is subject to 'a minimum of vibration and greatly reduces the possibility of microphonics in the system. The coaxial antenna is especially suited for continuous wave radar and as such allows the use of linear polarization rather than the more complex cross polarization or similar arrangements normally used.

The operation of this invention will be clearly comprehended from a consideration of the foregoing description of the mechanical-details thereof, taken in connection with the drawing and the above recited objects. It will be obvious that all said objects are amply achieved by this invention.

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

I claim:

1. An enclosed coaxial antenna, comprising: a generally parabolic receiver reflector having a receiver feed mounted substantially on the surface thereof and axially thereof; a smaller, generally parabolic transmitter reflector fixedly mounted concentric with and axially spaced from said receiver reflector; a flat plane reflector fixed between said transmitter reflector and said receiver reflector and positioned to reflect signal energy from the receiver reflector back to said receiver feed; a rigid dome structure structure peripherally fixed to said receiver reflector and to said transmitter reflector and fully enclosing both of said reflectors; and an electromagnetic energy isolating shroud extending axially from the periphery of said transmitter reflector beyond the outer surface of said dome structure.

2. An enclosed coaxial antenna, comprising: a generally parabolic receiver reflector having a flat central portion, and a receiver feed operatively mounted on said flat portion; a cylindrical support element fixed at one end to said receiver reflector and substantially enclosing said flat portion; a smaller, generally parabolic transmitter reflector operatively mounted adjacent the other end of and within said support element; a flat plane reflector fixed between said transmitter reflector and said receiver reflector and positioned to reflect signal energy from the receiver reflector back to said receiver feed; a rigid dome structure peripherally fixed to said receiver reflector and to said transmitter reflector and fully enclosing both of said reflectors; and an electromagnetic energy isolating shroud extending axially from the periphery of said transmitter reflector beyond the outer surface of said dome structure; a portion of said support element extending beyond said dome structure and constituting an electromagnetic energy isolating shroud surrounding said transmitter reflector.

3. An enclosed coaxial antenna, comprising: a generally parabolic receiver reflector having a flat central portion, and a receiver feed operatively mounted on said flat portion; a cylindrical support element fixed at one end to said receiver reflector and substantially enclosing said flat portion; a smaller, generally parabolic transmitter reflector operatively mounted adjacent the other end of and within said support element; a flat plane reflector fixed between said transmitter reflector and said receiver reflector and positioned to reflect signal energy from the receiver reflector back to said receiver feed; a rigid dome structure comprising a dome cap element fixed peripherally to said transmitter reflector and a dome ring element fixed peripherally to said receiver reflector and having an outer surface continuous with said dome cap, said dome ring being of different thickness from said dome cap; a portion of said support element extending between said dome cap and said dome ring beyond the outer surface thereof and constituting an electromagnetic energy isolating shroud surrounding said transmitter reflector.

4. An enclosed coaxial antenna, comprising: a generally parabolic receiver reflector having a flat central portion, and a receiver feed operatively mounted on said flat portion; a cylindrical support element fixed at one end to said receiver reflector and substantially enclosing said flat portion; a smaller, generally parabolic transmitter reflector operatively mounted adjacent the other end of and within said support element; a flat plane reflector fixed between said transmitter reflector and said receiver reflector and positioned to reflect signal energy from the receiver reflector back to said receiver feed; a rigid dome structure comprising a dome cap element fixed peripherally to said transmitter reflector and a dome ring element fixed peripherally to said receiver reflector and having an outer surface continuous with said dome cap, said dome ring being of different thickness from said dome cap; a portion of said support element extending between said dome cap and said dome ring beyond the outer surface thereof and constituting an electromagnetic energy isolating shroud surrounding said transmitter reflector; a feed operatively mounted adjacent said transmitter reflector; a waveguide communicating with said feed and extending externally of the antenna, said waveguide being fixed along its length to the inner surface of said dome structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,342,721 Boerner Feb. 29, 1944 2,413,187 McCurdy et al Dec. 24, 1946 2,430,568 Hershberger Nov. 11, 1947 2,460,869 Braden Feb. 8, 1949 2,625,678 Allison Jan. 13, 1953 

